Your Fall Weed Challenge: Winter Annuals in Your Orchard

Your weed problems for next year may already be in your orchard. Moist soils in the fall signal winter annual weed seeds to break dormancy and germinate.

What are winter annual weeds?

They are weeds with a growth cycle that begins in the fall. They grow from seed into a tiny rosette that lays flat on the soil. During the fall, they grow a small taproot and a few leaves before becoming dormant for the winter. Some stay green under the snow, ready for springtime.

When spring brings warmer temperatures, winter annuals will bolt a flower stalk early in the season. They flower and set seed in early summer, often shedding their seeds before the heat of the summer comes. By October, these seeds have either germinated or are waiting for fall rains to germinate.

Some weeds can be both summer annuals and winter annuals, like common chickweed and groundsel.

Why should we be concerned about winter annuals?

Winter annual weeds cause crop losses by reducing yields and interfering with harvest. They avoid our traditional weed management programs, causing extra expense to control them.

Winter annual weeds are very successful in orchards and other perennial crops. They are also more problematic wherever reduced tillage is practiced. Recently, more problems with winter annual weeds like Canada fleabane, garlic mustard, buttercups, shepherd’s purse and pepper grass have been observed.

The growth cycle of winter annual weeds gives them several advantages. Their growth periods coincide with periods of good soil moisture. They grow when crops do not need moisture or nutrients. Their small size at the rosette stage makes them inconspicuous, and they may be less susceptible to traditional weed control tools and timings. Plus, they often shed large numbers of seeds to help them survive the summer.

How can we control winter annuals?

Early fall gives us a window to prevent winter annuals from establishing in orchards. Mow field edges before seed shed to prevent winter annuals from moving into your orchard. Soil-applied residual herbicides applied in the fall can control the rosette stage, but should be applied either after harvest or within the preharvest interval where labeled.

What if winter annuals are already established?

Scout your orchards several times throughout the fall to know what to expect next spring. Plan to use early spring tillage or burndowns to destroy established winter annuals, but remember that the high range of herbicide rates may be needed as plants start to flower.

Winter annuals are not all bad! Remember that winter annual weeds can be effective ground cover to prevent erosion over winter. Where this is a concern, it is better to leave those rosettes for now - but be ready next spring!